A dress worn by the actress Keira Knightley at this year's Oscars was finally auctioned online for £4,301 on eBay yesterday.

One bidder from the United States topped dozens of potential buyers from around the world, all desperate to own a dress worn by one of the most sought-after actresses in the world.

The deep claret taffeta silk gown was custom-made by the designer Vera Wang for Knightley. The proceeds from its sale will go towards a £20m appeal launched by Oxfam to counter the humanitarian emergency in drought-hit east Africa.

Knightley, whose films include Bend It Like Beckham, Pirates of the Caribbean and Pride and Prejudice, had approached Oxfam personally with the gift. She said: "It's brilliant that this dress has raised this much. I know it will go a long way to help the people facing this food crisis in east Africa.

"Oxfam's teams are working hard to distribute food and provide clean drinking water, as well as giving longer term support to help people rebuild their lives."

An Oxfam spokeswoman said a flurry of last-minute bidding had pushed the price up from £3,800 to £4,301 in the final seconds of the auction.

Among the 48 bidders who unsuccessfully competed for the dress were a casino and a used-car salesman. During the time it was for sale, the website recorded 70,000 visits to the page.

The proceeds of the auction will provide enough food to feed 5,000 children for a month in Tanzania. An estimated 11 million east Africans face starvation in the drought that has hit nomadic herding communities in countries such as Kenya, Somalia and Tanzania.